The present invention relates to electric signal amplification circuits and, more particularly, to a programmable gain amplifier which may include an integrating preamplifier in a single circuit.
In some applications such as, for example, computerized tomography (CT) data acquisition systems (DAS), analog amplifiers are used to amplify small signals to within a predetermined range before coupling the signals to an analog-to-digital (A/D) converter. Amplifying the signals lowers the resolution needed by the A/D converter. U.S. Pat. No. 4,815,118, issued Mar. 21, 1989 and assigned to the assignee of the present invention, provides a discussion of programmable gain amplifiers and their use in CT data acquisition systems. As described therein, such programmable gain amplifiers have employed resistor switching or have used a plurality of amplifiers in parallel, each having a different gain and being individually selectable for a different gain setting. These prior art amplifiers have a settling time after a gain select, which is undesirable, and may also exhibit thermal and switching noise that can detrimentally affect circuit response.